1. Field of the Invention
The present invention relates to a communication system, and more particularly, to transmission system and method on a forward link in a communication system having a plurality of antenna arrays.
2. Background of the Related Art
In wireless communications, a desired signal (hereafter called an xe2x80x9coriginal signalxe2x80x9d), is received together with, in general, multiple interference signals. The level of distortion in a received signal caused by the interference signals is dependent on the ratio of power in the original signal to a sum of powers of the interference signals. Thus, where there are many interference signals, communication distortion occurs even if the power level of the original signal is substantially higher than individual levels of the interference signals.
Accordingly, a related art cellular communication system places emphasis on minimizing the interference signals, for example by using smart antennas. Thus, when a mobile terminal is in motion, or when an angle of reception at the mobile terminal otherwise varies, the mobile terminal may use an array of antenna elements to control phases of the array of antenna elements for detecting positions of distant signal sources. This approach enables selective transmission/reception of signals to/from the signal sources, selective transmission/reception of a particular signal (the original signal), and substantial reduction of interferences by minimizing influences from the interference signals.
FIG. 1 illustrates a related art transmission system with switching beam array antennas on a forward link. The related art transmission system is provided with a weighted vector storing part 101 for storing weighted vectors to produce a few fixed beams, a beam selector 102 for selecting a weighted vector from the stored weighted vectors and for providing the weighted vector to a beam former 103, and a beam former 103 for subjecting the weighted vector and a signal to be transmitted to a complex internal beam-forming process.
The communication system of the related art has many problems. For example, when one of the weighted vectors stored in the weighted vector storing part 101 for producing fixed beams is selected by the beam selector 102, and provided to the beam former 103 on a reverse link, the beam former 103 subjects the weighted vector and a signal to be transmitted to the complex internal beam forming process to produce and transmit an optimal beam on the forward link.
In application of the switching beam arrays to a TDD (Time Division Duplex) type mobile communication system, channel information obtained at a reverse link is applicable to a forward link, and a weighted vector obtained at the reverse link is applicable to the forward link, because a frequency of the reverse link is the same with the frequency of the forward link. However, because the frequency of the reverse link is different from the frequency of the forward link in the FDD (Frequency Division Duplex) type mobile communication system, phase information on the weighted vector are not the same. Therefore, direct application of the weighted vector obtained from the reverse vector to the forward vector will not provide an optimal beam pattern.
Moreover, where the channel environment of the mobile communication system changes rapidly, or when the reception angle of the signal changes rapidly, the related art method of using the switching beam, in which an optimal weighted vector that meets preset references is selected from a limited preset number of weighted vectors for producing a beam, can not provide a maximum gain to the original signal for an incident angle of the received signal. Instead, related art systems may provide too much gain to a noise component, resulting in less than optimal beam formation.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.
An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter.
Another object of the present invention is to provide transmission system and method on a forward link, which can form an optimal beam for varying channel environment in an FDD mode.
Another object of the present invention is to provide a system and method of minimizing noise on a forward link transmission channel.
In order to achieve at least the above-described objects in whole or in part, and in accordance with the purposes of the present invention, as embodied and broadly described, there is provided a communication system, including: a reception angle estimator configured estimate to a reception angle of a received signal; a determining part configured to determine a Quality of Service (QoS) parameter according to a service quality required by a subscriber of the received signal; a weighted vector calculator configured to calculate a weighted vector using the estimated reception angle and the QoS parameter; and a transmitter configured to apply the weighted vector to the signal to be transmitted.
To further achieve at least the above objects in whole or in part and in accordance with the purpose of the present invention, there is provided a method of transmitting a signal in a communication system, including: estimating a reception angle of a transmitted signal; determining a QoS parameter of the received signal; calculating a weighted vector using the estimated reception angle and the QoS parameter; and applying the calculated weighted vector to a signal to be transmitted.
To further achieve at least the above objects in whole or in part and in accordance with the purpose of the present invention, there is provided a method of transmitting a signal from a noise station, including: estimating a reception angle of a received signal from a first subscriber; determining a Quality of Service (QoS) parameter for the first subscriber; transmitting a transmission signal to the first subscriber by maximizing a gain in a desired signal direction and minimizing a gain in an interference signal direction in accordance with the estimated reception angle and the QoS parameter.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.